LFP FLA hybrid

[john61ct]

Originally Posted by rgleason

The basic question is what do you do about high current loads that should be disconnected when the LFP are low that will damage the relay.

Not requiring an addition control, if the contactors (relay vs solenoid) are designed to withstand 10-20% higher current than the maximum they will encounter.

So if you anticipate an occasional 450A, I'd go for a 500A rated contactor if from a vendor like Blue Sea.

If an unknown Chinese maker, maybe needs to be rated for double or more.

The good stuff isn't cheap.

[evm1024]

Continuing on with the block diagram I'm think of - I've added in some disconnects and such. Of course there are fuses and much more....

SD and HD are the obvious Start bank disconnect and house bank disconnect with J being the joiner between the start bus and house bus.

HVD add LVD are controlled by the LiFePO4 bank BMS.

In normal operation J is open and the black box takes care of joining the start bus and house bus when it is time to charge the House bank. Some post we will gt to the logic needed for the black box....

SD and HD are used to take their respective banks out of operation as needed.

In normal operation when the motor is running the black box joins the start and house buses. The alternator output charges the House bank to some limit (and runs house loads) and then disconnects the start form the house buses. At that point the alt continues to charge the start battery as "normal" while the house bank supplies the house loads in isolation from charge sources.

If you were to expect to motor for a long time (for example) you would then close the J switch which manually joins the start and house busses and open the HD switch which isolates the LiFePO4 house bank from the charge source. The House LiFePO4 bank just "floats", not connected to anything. (bad choice of word I know)

The Alternator supplied all house loads with power and in event of the failure of the alternator the start battery supplies the house loads.

You could close J and open SD which would put the alternators charge directly to the house bank "manually" and allow the house bank to start the engine if required.

Options have you.

Up next is a more complex diagram for other conditions..... In a day or few. Think about under what conditions the black box should join the start and house bus.

[rgleason]

Evm1024 Thanks.
Are SD, HD and J simple manual switches?

I like the ability to easily direct the alternator to either bank for starting. How would you wire the regulator power and sense wires?

Is there a good way to prevent me from screwing up the switchs somehow and discharging/overcharging LFP too much? --a distraction reminder?

[john61ct]

No, Alt should be hardwired to just one bank.

Automatic switch to get both charged together.

Ensure Alt can't be load dumped.

Manual switches if any to direct **load** feed, not charging.

[evm1024]

Originally Posted by rgleason

Evm1024 Thanks.
Are SD, HD and J simple manual switches?

I like the ability to easily direct the alternator to either bank for starting. How would you wire the regulator power and sense wires?

Is there a good way to prevent me from screwing up the switchs somehow and discharging/overcharging LFP too much? --a distraction reminder?

Yes, they are manual switches. Switches that are only changed when you go from one mode to another.

As John noted the common wisdom is to hardwire the Alt to a battery bank. And I do have my alt wired that way. I am exploring a different configuration in these drawings.

As noted you set the switches manually and leave them there for that mode of operation. There is no need to change the configuration in "normal" operation. The black box is what connects the 2 banks together and is responsible for monitoring the charge to LiFePO4 bank.

If you really were worried about opening the SB switch (start bank disconnect) then you could use a locking switch....

[evm1024]

Oh to your other question -

Because we are charging to LA profiles and the black box controls LiFePO4 charging (by joining the banks). The black box measures the LiFePO4 voltage at the LiFePO4 bank and disconnects the charge sources on the start bus from the house bus and thus the LiFePO4 bank.

To answer your specific question: The alternator regulator measures the voltage at the start bus.

[rgleason]

@evm1024 Looking forward to the next chapter..

Up next is a more complex diagram for other conditions..... In a day or few. Think about under what conditions the black box should join the start and house bus.

I think the black box should join the house bank when the voltage on the start bus has risen to 13.2v and LVD disconnect when the voltage has dropped below 12.8v provided the AGM/LFP start bank batteries are not sulfated and drawing too much energy. In this case, I think the LVD disconnect should occur at below 13.0v.

This all assumes the alternator regulator has been preprogrammed for LFP parameters according to the manufacturer. Balmar has 14.5v bulk and 14.4v for absorption for LFP batteries, which may be a little high, since most LFP are 90% charged at 14.2v, but I don't have real experience. Voltage meaurement is not really a good way to charge LFP and I think the BMS which knows about the SOC of LFP and the condition of all the cells, should be controlling this in the ideal world.

When should the HVD Disconnect occur (order of best control):
1. When the BMS sends a HVD disconnect alarm (30 seconds before disconnecting).
2. When the smart regulator with a shunt has determined that the charge current has decreased to 1%.
3. At some voltage between 14.2v and 14.4v (I don''t know what that should be yet.)


Looking forward to the next chapter. This guy charges at 14.0v and floats at 13.2v and has the LFP and FLA paralleled
Useful explanation of the Hybrid Lithium System by Hans Veldman on zwerfcat.